Conventionally, an energy storage device such as a lithium ion secondary battery is used as a power source for an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV) and the like. Such an energy storage device includes, in general, an electrode assembly, a current collector connected to the electrode assembly.
The electrode assembly which the energy storage device includes is formed by winding an element where a positive electrode plate and a negative electrode plate are arranged in a layered manner with a separator interposed therebetween, for example. When a conductive foreign substance such as a metal piece or metal powder, for example, intrudes into the electrode assembly having such a structure in which the positive electrode plate and the negative electrode plate are disposed in an opposedly facing manner, there is a possibility that a defect such as a minute short-circuiting occurs.
JP-A-2007-53002 discloses a method of manufacturing a battery having a structure in which electrode sheets of an electrode unit overlap with each other, and the electrode sheets projecting from the overlapping portion and current collector terminals are joined to each other by ultrasonic welding. According to this manufacturing method, by applying a compressive force to the overlapping portion of electrode sheets at the time of performing ultrasonic welding, it is possible to prevent metal powder generated during ultrasonic welding from intruding into the overlapping portion.
A conductive foreign substance such as a metal piece or metal powder in the inside of the energy storage device is generated in a manufacturing step such as welding between an electrode assembly and a current collector. However, the case where a conductive foreign substance is generated is not limited to such a case, and there may also be a case where a conductive foreign substance is generated due to an impact or the like applied to the energy storage device during the use of the energy storage device, for example.
Accordingly, even in the case where a foreign substance is generated in the inside of the energy storage device 10 due to an external factor after the manufacture of the energy storage device 10, it is important to prevent such a foreign substance from intruding (moving) into the inside of the electrode assembly for suppressing the occurrence of a defect.